1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor, and to an image forming method, an image forming apparatus and process cartridge therefor using the electrophotographic photoreceptor.
2. Discussion of the Background
Recently, organic photoreceptors (OPCs: organic photo conductors) have been widely used instead of inorganic photoreceptors for copiers, facsimiles, laser printers and their complex machines because of their good performances and advantages. Specific examples of the reasons include (1) optical properties such as a wide range of light absorbing wavelength and a large amount of absorbing light; (2) electrical properties such as high sensitivity and stable chargeability; (3) choice of the materials; (4) good manufacturability; (5) low cost; (6) non-toxicity, etc.
On the other hand, as image forming apparatuses become smaller, photoreceptors have smaller diameters recently. In addition, photoreceptors are required to have high durability as image forming apparatuses produce images at a higher speed and are free from maintenance. In this respect, the organic photoreceptor typically has a soft surface layer mainly formed from a low-molecular-weight charge transport material and an inactive polymer, and therefore the organic photoreceptor typically has a drawback of being mechanically abraded with an image developer and a cleaner with ease when repeated used in the electrophotographic process.
In addition, as toner particles has smaller particle diameters due to requirements for high-quality images, cleaning blades need to have higher rubber hardness and higher contact pressure for the purpose of increasing cleanability, and which also accelerates abrading photoreceptors.
Such abrasions of photoreceptors deteriorate electrical properties thereof such as sensitivities and chargeabilities, and cause abnormal images such as image density deterioration and background fouling. When a photoreceptor is locally abraded, images having black stripes due to defective cleaning are produced. Therefore, the following trials have been made to improve the abrasion resistance.
(1) Japanese Laid-Open Patent Publication No. 56-48637 discloses a photoreceptor using a hardening binder in its surface layer; (2) Japanese Laid-Open Patent Publication No. 64-1728 discloses a photoreceptor using charge transport polymer material; (3) Japanese Laid-Open Patent Publication No. 4-281461 discloses a photoreceptor having a surface layer wherein an inorganic filler is dispersed; (4) Japanese Patent No. 3262488 discloses a photoreceptor having a protection layer including a hardened multifunctional acrylate monomer; (5) Japanese Patent No. 3194392 discloses a method of forming a charge transport layer using a coating liquid formed from a monomer having a carbon-carbon double bond, a charge transport material having a carbon-carbon double bond and a binder resin; and (6) Japanese Laid-Open Patent Publications Nos. 2000-66425 and 2004-212959 disclose a photosensitive layer including a hardened positive hole transport compound having two or more chain polymerizing functional groups in the same molecule.
Although the abrasion resistance has been more improved than that of the conventional photoreceptors thereby, there rises a new problem. The conventional photoreceptors do not produce defective images for long even when having foreign particles or damages on the surface thereof because of being refaced by the abrasion. However, the improved photoreceptors continue to produce defective images for long once having foreign particles or damages on the surface thereof.
Particularly, the recent toners having a smaller particle diameter and a low softening point for producing higher quality images and saving energy include inorganic particulate materials such as silica to improve the fluidity in many cases. The silica occasionally sticks in the surface of the photoreceptor and the toner constituents such as wax accumulate around there, resulting in production of white-spotted defective images.
Furthermore, in order to produce much higher quality images and have higher durability, the photoreceptor needs to have much higher abrasion resistance and much less residual potential.
Because of these reasons, a need exists for a long-life photoreceptor, having good abrasion resistance and electrical properties, and producing less white-spotted defective images.